1. Field of the Invention
The present invention relates to a lifting column, preferably for height-adjustable tables, the column consisting of sections of pipe profiles telescopically arranged inside each other, with slides arranged between the individual sections, and the invention also relates to a method of manufacturing such a column.
2. The Prior Art
The focusing in recent years on working environment has resulted in a trend toward the desirability of making also common work tables, such as desks, adjustable in height, in addition to more sophisticated tables and equipment. This means that the cost of the height adjustment is a decisive factor. As a result, a new field of products has emerged, viz. lifting columns for tables, where it is intended to meet the specific requirements that are associated with tables.
The columns are usually made from steel pipes or/and extruded aluminium pipes which are cut to desired lengths. The individual sections have interposed between them slides of plastics in the form of bushings and/or separate bricks, and there are also examples of slides in the form of axially extending strips.
From an overall point of view, the pipes are vitiated by two inherent drawbacks. One drawback is a relatively great dimensional tolerance, which results in great variations in the gap between the sections. This in turn means that a relatively great play may occur between the sections. The play causes the table to be unstable, which is impermissible from a user point of view. Machining of the pipes to reduce the dimensional tolerances will make the columns unacceptably expensive.
Adjustable slides have been developed to avoid the play, which may be adapted to the current width of gap, cf. e.g. DK 171 903 B1, DE 298 12 762 U1. In both cases, machining of the sections is required, and DE 298 12 762 U1 additionally requires a special configuration of the sections. In the first-mentioned case, holes have to be drilled and threads to be made for the adjustment screw of the slides, and in the last-mentioned case transverse grooves for the central rib of the slides have to be made internally in the sections. This, of course, adds to the costs of the columns.
The other drawback is that during the manufacturing process the pipes may be twisted around their longitudinal axis, which means that the cross-section is out of angle. This causes the gap between two sections to be non-uniform, unless by chance they have the same angle of twist. Not only does the gap have a non-uniform width, but it will also vary depending on how much or how little the two sections are twisted relative to each other. It gets even worse if two sections are twisted in their separate directions. The object of the invention is to provide a lifting column of the type stated in the opening paragraph with simple slide devices, simple mounting of these and without noticeable machining of the sections.